1. Field of the Invention
The present invention relates to a particulate catalyst for use in a fluidized bed in a vapor phase reaction, which catalyst is endowed with an extensively reduced loss of catalyst particles, particularly, those having a smaller particle size, and can suppress the reduction of the yield of a desired product due to the deterioration of the fluidized state of a fluidized bed.
2. Background Art
Particulate catalysts employed in reactions of a vapor phase in a fluidized bed are generally required to be excellent in catalyst strength as well as catalyst activity. As the test of the strength of a fluidized bed catalyst, a test method of attrition-resistant properties in accordance with the ACC method (American Cyanamid Co. Ltd. 6/31-4m-1/57, "Test Method for Synthetic Fluid Cracking Catalyst") has been used. The values of the attrition-resistant properties according to this test method have been used as a standard for judging the applicability of a catalyst to a fluidized bed reaction, that is the degree of catalyst loss in a reactor. In their applications to practical reactor, the attrition-resistant properties, however, do not always correspond to the loss of a catalyst.
Furthermore, there have been proposed a variety of explanations for the main cause of loss of particulate catalysts. None of these explanations have become established theory. Among them, there have been proposed, as the main cause of catalyst loss, the crushing or attrition of catalyst particles due to the jet gas flow at spargers of a reactor, or the collision or attrition between catalyst particles with each other, and between catalyst particles and a reactor wall or internal components.
However, irrespective of the causes, it is the inventors' belief that catalyst particles in a fluidized bed reactor tend to be crushed or worn more easily if the particles have a finer particle size, so that the strength of particles having a smaller diameter is particularly important and has to be taken into consideration in order to reduce the catalyst loss. However, as far as the present inventors know, no improvements of techniques have been proposed regarding this point.
By way of example, while the strength of a single catalyst particle alone is referred to in Japanese Patent Laid-Open Publication No. 262753/1993, nothing is indicated about the strength of the finer particles or the catalyst loss with only exception of the breaking load of particles having a particle size of 88 to 150 .mu.m. Also, only the crushing strength of a catalyst is described in Examples of Japanese Patent Laid-Open Publication No. 144132/1995.
The object of the present invention is to provide such a particulate catalyst for use in a fluidized bed that the catalyst loss can be reduced whereby the particle size distribution can be maintained in an appropriate range and the reaction can also be maintained at a high level without lowering the contact efficiency.